Campbell Scientific AVW200-series Vibrating Wire Interfaces - Manual (Page 63)

AVW200-series 2-Channel Vibrating Wire Spectrum Analyzer Modules
Power supply must be able to sustain at least 9.6 V (datalogger minimum)
even during 75 mA transmitter bursts lasting only a few milliseconds.
4. Lightning damage to RF401 or AVW206
Swap in a known good RF401 or AVW206 with the same settings and see
if this cures the problem. Lightning damage can occur leaving no visible
indications. A “near miss” can cause damage as well as a more direct hit
with evidence of smoke.
5. Lightning damage to antenna and/or cable
Swap in a known good antenna and/or cable. Hidden damage may exist.
6. Moisture in coaxial antenna cable
It is possible that moisture has penetrated inside the plastic sheath of the
coaxial cable. Water inside the cable can absorb RF energy and attenuate
the transmitted signal; the received signal would also be attenuated. It is
difficult to dry out the interior of a coaxial cable. Substitution of a dry
cable is recommended.
Placing a wet cable in a conventional oven at 160°F for a couple of hours
should dry it out. Shield the antenna cable against damage from radiated
heat from the oven element by placing the coiled cable on a large cookie
sheet or a sheet of aluminum foil. See Section 5.3.2 (3.d) for information
on weatherproofing the antenna cable.
7. AVW206 receiver “de-sensing” from nearby transmitter
This problem can be observed from LED behavior when operating a hand-
held radio near an AVW206 that is receiving collected data from a remote
station. If you key a hand-held 150 MHz or 450 MHz transmitter, even
though its frequency of operation is far removed from the 900 MHz band,
its close proximity to the AVW206 can overwhelm (de-sense) the
AVW206 receiver resulting in failed packets and LoggerNet retries. This
problem could also occur if you located an AVW206 at a site containing
commercial transmitters or repeaters. In general it is best to avoid such
sites, especially the high-power FM or AM transmitter antenna sites
which can change at any time with added equipment.
It is possible to avoid de-sensing in some cases if the RF link is solid
enough due to: the proximity of your remote AVW206(s); high antenna
gains and directionality; high elevation; and sufficient distance separation
between AVW206 and commercial transmitter antenna. Try horizontal
polarization of antennas. A field test in such situations is essential.
8. Insufficient signal strength
There are some things you can try to get that extra few dBs of signal
strength sometimes necessary for a dependable RF link. The drop in
signal going from Winter (no deciduous tree leaves) to Spring sometimes
requires a little more signal.
a. Raise the antenna height using a mast, tower or higher terrain. Often
a little extra height makes the difference.
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